1. Field of the Invention
The present invention relates to a key switch signal recognition circuit, and more particularly to a simple circuit layout of key switch signal recognition circuit.
2. Description of the Prior Art
Key switch circuits are intensively used in office automation equipment, industrial instrument, electric and electronic consumers products, and electric home appliances to serve as input interface means between the user and the machine. According to the conventional key switch circuit designs, one key switch button is matched with one circuit loop. The key switch buttons can be switches, micro switches, and membrane switches.
FIG. 1 shows a prior art switch button type key switch signal recognition circuit including a number of key switches. According to this design, a number of key switch contact areas may be arranged on a substrate 10 such as a printed circuit board, and a number of key switch buttons 11 are suspended above the key switch contact area. Each key switch contact area is generally formed of two corresponding copper foil wires 12 and 13. One copper foil wire 12 is connected to a common point, such as a grounding terminal or a power source terminal. The other copper foil wire 13 is connected to a first connector 14. The pins of the first connector 14 are respectively connected through a cable 15 to a second connector 17 mounted on a circuit board 16. The second connector 17 of the circuit board 16 is further connected to a key switch signal reading interface 18 or a key switch signal processing circuit. According to this conventional key switch circuit design, a number of independent circuit loops are needed to transmit click signal from the key switch buttons, the cable 15 must have a number of wires, and the connectors 14 and 17 each must have a number of pins and one grounding wire. Further, when the numbers of the key switch button are changed, the model of the connector, the number of wires of the cable, and the number of pins of the key switch signal reading interface must be relatively changed.
In some key switch circuit designs, an encoder is used to achieve the object of using a limited number of wires to recognize a number of key switch buttons. However, the use of the encoder greatly increases the cost of the key switch circuit. Therefore, these conventional key switch circuit designs do not satisfy current market requirements. For example, in the design of a key switch circuit for a scanner, the factors of ease of use, highly expandability, less number of component parts, and lost cost must be taken into account.
Therefore, it is desirable to provide an improved key switch signal recognition circuit to mitigate and/or obviate the aforementioned problems.